NAME

       nbd_aio_pread_structured - read from the NBD server

SYNOPSIS

        #include <libnbd.h>

        typedef struct {
          int (*callback) (void *user_data, const void *subbuf,
                           size_t count, uint64_t offset,
                           unsigned status, int *error);
          void *user_data;
          void (*free) (void *user_data);
        } nbd_chunk_callback;

        typedef struct {
          int (*callback) (void *user_data, int *error);
          void *user_data;
          void (*free) (void *user_data);
        } nbd_completion_callback;

        int64_t nbd_aio_pread_structured (struct nbd_handle *h,
                                          void *buf, size_t count,
                                          uint64_t offset,
                                          nbd_chunk_callback chunk_callback,
                                          nbd_completion_callback completion_callback,
                                          uint32_t flags);

DESCRIPTION

       Issue a read command to the NBD server.

       To check if the command completed, call nbd_aio_command_completed(3).  Or supply the
       optional "completion_callback" which will be invoked as described in "Completion
       callbacks" in libnbd(3).

       Note that you must ensure "buf" is valid until the command has completed.  Furthermore, if
       the "error" parameter to "completion_callback" is set or if nbd_aio_command_completed(3)
       reports failure, and if nbd_get_pread_initialize(3) returns true, then libnbd sanitized
       "buf", but it is unspecified whether the contents of "buf" will read as zero or as partial
       results from the server.  If nbd_get_pread_initialize(3) returns false, then libnbd did
       not sanitize "buf", and the contents are undefined on failure.

       Other parameters behave as documented in nbd_pread_structured(3).

       By default, libnbd will reject attempts to use this function with parameters that are
       likely to result in server failure, such as requesting an unknown command flag.  The
       nbd_set_strict_mode(3) function can be used to alter which scenarios should await a server
       reply rather than failing fast.

RETURN VALUE

       This call returns the 64 bit cookie of the command.  The cookie is ≥ 1.  Cookies are
       unique (per libnbd handle, not globally).

ERRORS

       On error "-1" is returned.

       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

HANDLE STATE

       The handle must be connected with the server, otherwise this call will return an error.

VERSION

       This function first appeared in libnbd 1.0.

       If you need to test if this function is available at compile time check if the following
       macro is defined:

        #define LIBNBD_HAVE_NBD_AIO_PREAD_STRUCTURED 1

SEE ALSO

       nbd_aio_command_completed(3), nbd_aio_pread(3), nbd_create(3),
       nbd_get_pread_initialize(3), nbd_pread_structured(3), nbd_set_pread_initialize(3),
       nbd_set_strict_mode(3), "Issuing asynchronous commands" in libnbd(3), libnbd(3).

AUTHORS

       Eric Blake

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2019-2021 Red Hat Inc.

LICENSE

       This library is free software; you can redistribute it and/or modify it under the terms of
       the GNU Lesser General Public License as published by the Free Software Foundation; either
       version 2 of the License, or (at your option) any later version.

       This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU Lesser General Public License for more details.

       You should have received a copy of the GNU Lesser General Public License along with this
       library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
       Floor, Boston, MA 02110-1301 USA